1. Field of the invention
This invention relates to a process for preparing fluid cracking catalysts (FCC) and more particularly sol based faujasite containing catalysts by adding acid stable surfactants to the component streams prior to the spray drying step. This addition results in a catalyst that has superior density and hardness characteristics.
Although the surfactants may be added into any of the component streams, the greatest improvement in properties of the catalyst are achieved when the surfactants are added to all component streams prior to spray drying.
2. Description of the Prior Art
Molecular sieve-type cracking catalysts have been in use since 1962, when Plank and Rosinski (U.S. Pat. Nos. 3,140,249; 3,140,253; 3,210,267; 3,271,418; 3,436,357; 3,459,680) first introduced them. The rapid acceptance by the petroleum refining industry, world-wide, was due in large part to the significant increase in gasoline yield and improved coke selectivity obtained with zeolite containing catalysts as compared to catalysts based upon amorphous silica-alumina.
The first catalysts introduced were based upon the incorporation of rare earth stabilized faujasite with silica-alumina ratio's between 2.5 and 3.0. These early formulations were simply admixtures of zeolite-molecular sieves with the amorphous silica-alumina and clay-synthetic gel materials previously used alone as cracking catalysts. That is, prior to spray drying, the molecular sieve component was added typically to the gel slurry. The rapid initial success of these types of catalysts and the potential they afforded for yield and operational benefits resulted in the petroleum refining industry demanding FCC catalysts containing molecular sieves with even higher silica-alumina ratios; i.e. molecular sieves approaching silica-alumina ratio of 5; because this ratio material imparts superior thermal and hydrothermal stabilities. This demand was further stimulated by the high temperature regeneration technology introduced in the mid- seventies and described in U.S. Pat. No. 3,844,973, and the almost simultaneous development of combustion promoter additives for regeneration of FCC catalyst described in U.S. Pat. No. 4,072,600.
Acceptance of these technologies by the refining industry demanded catalyst with molecular sieves of higher silica-alumina (faujasite type) ratio with higher maintenance of cracking activity (stability) due to the more severe operating conditions to which the catalyst was subjected.
Presently, the removal of lead from gasoline has further sustained the world-wide demand for high silica-alumina ratio sieves. This is due to the improvement in gasoline octane which can be obtained catalytically by converting high silica-alumina ratio molecular sieves into a modified form known as ultrastable-Y or USY type materials. The ultrastable form of Y-zeolite can be achieved by conversion of the sodium form of Y-zeolite (faujasite) before incorporation into the catalyst or the entire catalyst particle can be treated, under conditions which result in an in-situ conversion of faujasite within the microsphere itself. It had been observed that the higher the silica-alumina ratio of the starting NaY zeolite, the higher the quality and performance of USY prepared either ex-situ or insitu. The same phenomenon is noted in the molecular seives sold under the trade name LZ 210 type molecular sieves by Union Carbide Corp.
The use of a silica-sol type binding system in the preparation of zeolite promoted catalysts has been described in U.S. Pat. No. 3,867,308 and alum buffered silica-sol have been described U.S. Pat. No. 3,957,689.
Catalysts based on sol technology for the binding system were developed in response to an increasing demand for harder and denser catalysts to meet the ever tightening environmental constraints being placed on the petroleum refining industry. There are a number of other related patents describing processes for preparing molecular sieve type catalyst; e.g. U.S. Pat. No. 3,425,956. These patents are typical of the large body of art in this area.
With the introduction of sol bond catalysts, significant improvements in density and hardness were immediately apparent. These new catalysts, however, still left considerable room for additional improvement. Namely examination by Scanning Electron Microscopy (SEM) revealed that almost every microspheriodal FCC catalyst particle possesed a "blow-hole" or a cavernous region which made them much more susceptible to break into two or more smaller fragments during the FCC operation. When this occurs the smaller fragments are almost instantly lost via the regenerator flue gas stack. If the breakage occurs on the reactor side, the slurry oil stream becomes over-loaded with catalyst dust referred to as fines. If the condition continues for any appreciable length of time it can result in the total shut down of the FCC unit. Such a shut down is extremely costly to the refinery both in terms of lost product and unscheduled maintenance. The "blow-holes" can be reduced by changes in the catalyst manufacturing process. These process changes are not necessarily easy or always economical. Even after the conventional process scheme changes the "blow-hole" problem is not necessarily eliminated.
It is the purpose, therefore, of our invention to show that the "blow-hole phenomenon" (cavernous openings and the shell character of micropheriodal particles) can be effectively eliminated by the selective use of acid stable surfactants.
This treatment does not negatively affect the catalytic activity and selectivity. It might be argued that the improved morphology improves the reactivity of the catalyst.